Safety switch



April 28, 1953 J. w. HUNT 2,636,953

SAFETY SWITCH Filed Feb. 25, 1950 2 SHEETS-SHEET 1 INVENTOR.

, Jon W. HUNT A from/5y Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE SAFETY SWITCH John V Hunt, Pontiac, Micl1., assignor of onehalf to Walter P. Barrett, Pontiac, Mich.

10 Claims.

The present invention relates to electric switch units andv constitutesv an. improvement over switches of the. type disclosed in my co-pending application No. 34,462, filed June 22, 1948. My co-pending application relates to load-carrying safety switches adapted for supporting the fixed end of a hoist cable and for automatically stopping the downward movement of the hoist block when the tension in the cable falls below a predetermined minimuzn.

It. is desirable for switches of the type shown in my co-pending application as well as other types ofsuch switches to include a safety feature to protect the switch units and hoist equipment from iniury resultim from lifting loads in excess of the designed maximum load-carrying capacity of the hoisting equipment. Overloading in this manner may cause injury to personnel and also may cause serious damage to the equipment resulting in excessive. maintenance costs and further resulting in, prolonged periods. of idleness while repairs are being made.

Accordingly, it is an. object of the present invention to provide an improved electric switch unit suitable for use with hoisting equipment and which is adapted to stop. operation of the hoist motor when a loadabove a predetermined amount is placed on the hoist, cable, thereby to prevent damaging the hoisting equipment, and further,

which is adapted. to stop downward unwinding movement of' the. cable-winding drum whenever the tension in the cable falls below a predeterminedminimum, thereby to stop. unwinding of the cable so to prevent slack forming therein.

It is a further object of the present invention to. provide. an improvedv electric switch unit suitable for. use with hoisting equipment, conveyor drivev units, winches, and the -ke, to prevent overloading thereof, which includes means for making small. adjustments of the. overload limit andwhich is adapted topermit relatively greater adjustment of the overload limit by interchanging of spring biasing means therein.

It is still a further object of. the present invention to provide. a combined overload and downward. control, switch. unit whichis charac. terized by its: simplicity. sturdiness, and adaptability'for use with hoistingequipment, and which is, constructed and arranged to-permit repairing thereof when necessary in a most efficient and.

economicalmanner.

Other objects of. this. invention will. appearv in the. following description and appended claims, reference, being hadto. the accompanying drawings forming a part of this specification wherein 2 like reference characters designate corresponding parts in the several views.

In the drawings:

Fig. l is a longitudinal sectional View of one form of overload and downward control switch of the present invention.

Fig. 2 is an end View of the overload and downward control switch shown in Fig. l with a section broken away.

Fig. 3 is a plan view of an electric hoist showing a combination overload and downward control switch installed in its operating position.

Fig. 4 is a longitudinal sectional view of an. other form of overload switch of the present invention.

Fig. 5 is a fragmentary sectional view of still another form of the control switch.

Before explaining the present invention in detail it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and-of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to Figures 1 and 2 of the drawing, a combination overload and downward control switch it] can be seen which includes a housing i2 having a left housing section l4 and a right housing section It. The housing sections l4- and it are suitably secured together as by welding at IS. The housing 12 is generally cylindrical in shape and has its one end closed by a cap member 2a which is secured thereto by a plurality of bolts 22. The other end of the housing 12 is closed by an adjustable overload nut 24 which is threadedly connected to the housing 12 and held in a fixed position therein by a set screw 28.

Threadedly connected within the overload nut 24 is a downward control adjustment nut 28held in a fixed position therein by the set screw 30. A bushing 32 extends axially through the downward control adjustment nut 28 within which is journaled a load shaft 3 2'. The shaft 34 is journaled at its other end in the cap member 20.

An oil seal is provided in the cap member 201 which includes a plate at secured to the cap member 20 by a plurality of screws 38 and an:

oil seal gasket 40.

The load shaft 34 has a load nut 42 threadedly secured thereto and locked against movement by, a cotter pin M. Mounted on the load shaft 34" on one side of the load nut 42 is a thrust bearing Q8. On the other side of thrust bearing 46 is a load plate 48. The load plate 48 has rigidly secured to its one side a cam 56 which is adapted to actuate either an overload switch or a downward control switch in the control circuit of a hoist motor as will be more fully described hereinafter.

The load plate 48 has a recessed portion 52 formed therein adjacent the load shaft 54 and within which is seated a downward control spring 54. The downward control spring 54 has its other end seated against the downward control adjustment nut 28. Thus, it can be seen that the downward control spring 54 acts to bias the load plate 68 to the left, as seen in Fig. 1, to the unloaded position thereof. When in this position, the load plate 38 will be abutted against the annular stop 56 of the cap member 29. It is believed understood from the above description that when a load is placed on the load shaft 34, moving it to the right, the load nut 42, thrust bearing 36, load plate 48, and cam 50 will all be moved a corresponding amount to the right with the load shaft 34. In a similar manner, when the load is removed from the load shaft 3% the downward control spring 54 will bias the load plate 48, cam 50, thrust bearing 46 and load nut 42 to the left to the unloaded position of the load shaft 3 Mounted on the outside of the housing i2 is a switch housing 58 adapted to house any form of conventional switch. In the present modification of the invention, two conventiona1micro-switches Ed and 52 are shown. A fitting B l is shown on one side of the housing 58 through which electric leads (not shown) may be extended to said switches from the electric controls for a hoist motor.

The electric switch 60 is in a circuit adapted for controlling the downward hoisting of the hoist motor. The switch 60 can be actuated by means .Of a cam follower 66, which is adapted to follow on the cam 50. When the cam 50 is in its unloaded position, as seen in Figure l, the cam fo1 lower 66 will actuate the switch 60 to prevent unwinding action of the hoist motor, and thereby prevent 1owering of the hoist cable. When a load is placed on the hoist cable, which will be transmitted to the load shaft 32 causing movement thereof, the cam 56 will be moved to the right, and after the cam follower 66 has moved a predetermined distance down the inclined surface 88 of the cam 50, the switch 60 will be actuated closing or opening the said circuit, as necessary, to permit the hoist motor to hoist downwardly. The load necessary to move the cam sufficiently far to this predetermined position will depend upon the strength of the downward control spring 54 and the adjusted position of the downward control adjustment nut 28. If desired, this load may be equivalent to the weight of the hoist block and hook of the hoist cable. In this manner, the hoist will be ready for use whether or not a load is placed on the cable hook. However, if during the lowering operation the load on the cable should be reduced below this predetermined minimum, the downward control spring 5d will bias the cam 50 to the left causing the switch fill to be actuated to stop the downward action of the hoist motor. Thus, it can be seen that a downward control switch for a hoist motor is provided which will prevent slack from forming in the hoist cable when any obstruction is met by the load on the cable preventing the downward movement there of.

If it is desired to vary the amount of the predetermined minimum load necessary to actuate the switch 60, this can be accomplished by substituting for the downward control spring 54 another spring having different load characteristics or by adjustment of.the downward control adjustment nut 28. When only slight adjustments of the minimum predetermined load are desired, this can be accomplished by loosening the set screw 30 and by increasing or decreasing the tension in the downward control spring 54 by screwing the downward control adjustment nut 28 in or out, respectively. However, if greater changes in the predetermined minimum load are required than can be made by adjustment of the downward control adjustment nut 28, a new spring can be substituted for the downward control spring 54 merely by removing the cap member 20, load nut 42, thrust bearing 46 and load plate 48.

The present form of the invention also includes an overload control mechanism for preventing upward hoisting action by the hoist motor when a load above a predetermined maximum has been placed on the hoist cable. This mechanism includes an overload plate I'll, mounted on a bushing #2 for axial movement in the housing [2. An overload spring 7 4 is seated at its one end against said overload plate 10 and at its other end against the overload nut 24. The overload spring 14 acts to bias the load plate l0 against a bearing assembly 16. When in the normal position, shown in Figure l, the overload plate '59 has an inclined shoulder 18 which is spaced from a corresponding inclined surface on the inner wall of the housing 12. The overload spring 74 is designed to have sufficient strength to maintain the overload plate 10 and the housing H2 in this spaced relation whenever loads below the predetermined maximum are carried by the hoist cable. When an overload is placed on the hoist cable, the overload spring 14 will be collapsed by the load exerted thereon through the load plate 70. The overload is transferred to the overload plate 70 in the following manner:

When a load is placed on the load shaft 34, the cam 50 will be moved to the right in the slot 78 of the bearing assembly 76. Also, the load plate 48 will be moved a corresponding distance therewith as was previously described. If an excessive load is placed on the load shaft 34, the inclined surface 80 of the load plate 48 will come into engagement with the inclined surface 82 of the overload plate it. Thus, if an overload is placed on the shaft 34, this overload will be transferred from the load plate 48 to the overload plate lii causing the spring 74 to be collapsed, resulting in the movement to the right of the load plate 48, the cam 50 and the overload plate 10. The overload switch 62 is adapted to be actuated by a cam follower 81 which follows on the cam 59. ,The overload switch 62 is designed to be actuated when the cam follower 87 has progressed down the inclined surface 68 of the cam 56 beyond a predetermined position. Thus, it can be seen that a safety mechanism has been provided for the electric hoist whereby upward hoisting action of the electric motor will be stopped if an excessive load has been placed on the hoist cable.

If it is desired to change the overload limit of this switch unit, this can be accomplished either by adjusting the overload nut 24 or by substituting for the overload spring 14 a spring having different load characteristics. Adjustment of the spring 14 can be made simply by loosening the set screw 26 and screwin the overload nut 2; use, one

in, or out depending upon whether it is: desiredto tighten or loosen the overload spring i l. 11? anew overload spring is to be substituted for the overload spring M, this can be accomplished by removal-of the cap member 26 and various elements necessary to slide the overload spring 14 off the load shaft 34-. Thus, it can be seen that suitable means are provided whereby" the switch mechanism may beset to operate at any desired overload limit.

As-previously' stated, any form or conventional switch may be used with the present-combination overload and downward control switch unit. There is very little danger of any damage being done to' these switches during the operation of the combination overload and downward control switch unit; As can beseen, none-of the load placed on the shaft 34 will be carried by the switches 66 and 612. If the switches do becomedefective for any reason, new switches can be substituted therefor without any" appreciabledelay merely by removal of the cover plate 84: of the housing 58'.

The present form of the invention is adapted to be used either as a pull-type combination overload and downward control switch or as a push-- type combination overload and downward con-- trol switch. At the one end of the load shaft 3d is an eye 3% to which a cable orthe likeinay be attached for applying a load to load shaft 34. The other end til of the load extends outwardly through tli'e cap member 26 to permit the shaft 3 3 to be actuated by a pushing action against the end 838. This latter feature was developed to eliminate the-necessity or" fastening the load shaft directly to the hoist cable sothat this combination switch unit will be adapted for use with any form of hoist cable resting. It is believed to be apparent that pull type switch cannot be used, for example, with a hoist cable reeving having one rope, one part single; since in this reeving one end of the cable will be secured to the drum on which the cable is wound and said cable will extend directly from said drum to its other end which will have theblock' and hook attached thereto. Thus, there will be no place on the cable to which the eye of the load shaft 3d could be operatively connected. However, the pusher type' switch can be used with any hoist-cable reeving sin-ce-thelead shaft 3d can be actuated by a worm gear or the like suitably driven from the cable drum;

when the present invention is used as a pull type switch, suitable means are provided permitting the load shaft 34 to rotated within the housing !2: f a turning moment is applied to the eye dd, the load shaft 3 and the load nut' lil will turn on the thrust ball bearing ill; The re mainder of the elements within the housing 42 will be held against rotation by'the S3 wl'iich is movable only in an axial direction in the slot 78 of the bearing assembly it. The iatteris se curely mounted against rotation i. hin he housing' l2:

Referring now to Figure 3 of the drawings; a pull-type combination overload and downward control switch iii can be seen mounted on electric hoist unit The electric hoist unit 33 has an electric motor {it at its one end and a braking unit 92 at its othe Disposed betv eenthe electric motor Qt and the brake unit 22 is a drum suitably housed, on which is wound'a cable 96' which is connected tov the eye 83 of the load" shaft fi l by a suitable: reeving". Mounted on the housing of the electric r. I34 and the cam E35.

hoistunit is an electric'control box 91; which is connected to the pull-type control switch it by a conduit 83.

In'Figure 4 of the-drawings, a modified form of the present invention can beseen; This form ofthe invention is a simplification of the form of the invention shown in Figures 1 and 2 and includes only the overload switch thereof. A housing 5 ll!" is provided which is closed at its one endby atransfer-member H2 and at its other end by an overload adjustment nut H4; The

latter is threadedly connected to the housing 2 itand is locked in place therein by: the set screw H6.

is journa-leda load shaft I29". Theload shaft lfiil is journaled at its other end in a bushing 12? extending through the transfer member H2. The latter-is threaded y connected tothe housing IN!" to permit axial adjustment t. .ercin for purpose to behereinafter described and is locke inplace by a se screw its; A closure plate {'25, held to the transfcrmember M2 by a plurality of screws I28, encloses the end of theload shaft Threadedly connected to the load shaft 523 is a load nut lilo which is locked to the said shaft I20- by a set screw i132. Forward of the load nut i3il'is a stop member !34 adapted to engage the end of the travel member H2 On the forward face of the stop member (34 is an annular cam 36 which is secured. thereto by any suitable means such as welding, iorexample. .Asn overload spring 3-33 is seated at its one end against said stop member its and at its other end against said overload nut lid. The overload spring ltt acts to bias the stop member Md and the care I35 to the inoperative position shown in- Figure 4.

Moon ed on the housing H6 is a switch housins H85! suitably constructed tohouse any form of conventional switch for causing an electric hoist motor to be tie-energized when an overload is placed on the hoist cable; In the housing its, a conventional micro-switch i i-2 is shown which is adapted to be actuated by a cam follower its in response to movement of the earn 1 As indicated above, any form of conventional switch can be used in the present form of the overload switch unit. When the switch hi2 has been installed in the unit, proper adjustment can be made so that the unit can be effective to me vent hoisting action of the electric motor at any desired overload limit. This can be done by selecting an overload spring i333 of suitable strength and by properly adjusting the overload adjustment nut lid, as was explained above with respect to the corresponding parts of the form of the invention shown in Figures 1 and 2; In the form of the invention shown in Figure 4, an additional adjustment feature is provided by the-transversemember H2". As can be readily seen from the drawings, when the transfer member H2 is moved axially in or out, a new stop position Will be provided for the stop member Thus, the overload switch H0 can be easily used with any switch i 52, andif it becomes necessary-to replace the electric switch M2, this can be-done and overload sw eh i N can be adjusted to conform to the new switch M2 so that the same operating characteristics of the overload switch unit will be provided.

The modification shown in Figure L is a pulltype overload control switch and has an eye MB on; theload shaft 128 for attaching the hoist cable. Provision is made in this unit to allow A bushing lit extends axially through the overload adjustment nut H4 and within which the load shaft l 20 to rotate, if rotation movement is imparted to it by the cable. When the load shaft I20 is rotated, the load nut 130, stop member I 3 and cam I36 will all be rotated therewith. Since the cam is annular in shape, the cam follower I34 will be actuated in the same manner whether the cam is being rotated or stationary.

Another modification of the present invention is shown in Figure of the drawings. This form of the invention is very similar to that shown in Figure 4 and like reference numbers are used to indicate like parts. This form of the invention shows a push-type control switch in contrast to the pull-type shown in Figure 4. In this form of the invention, the load shaft I20 extends axially through the travel member H2A and is adapted for actuating the overload switch unit in response to a pushing action on the outer end of the load shaft I28. This form of the invention has the advantage that it can be used with any type of reeving as was explained above in the description of the modification of the invention shown in Figures 1 and 2.

It should be understood that the modified forms of the invention shown in Figures 4 and 5 can be adapted for use either as a downward control switch or as an overload switch. When it is desired to use this type of control switch for downward control purposes, a suitable spring :38 must be used and the switch M2 must be in the downward control circuit and must be one which will cut off power to the hoist motor during downward hoisting in response to movement of the cam follower 544 a predetermined distance down the inclined surface of the cam E36. Whereas, when this type of control switch is used as an overload control switch, a stronger spring I38 must be used and the switch must be in the control circuit for controlling the upward hoist ing of the motor and must be responsive to movement of the cam follower i i l a predetermined distance up the inclined surface of the cam H6. Having thus described my invention, I claim: 1. A hoist control switch adapted for stopping the upward hoisting action of a hoist motor when load on the cable of the hoist exceeds a predetermined amount, said switch comprising a housing, a load shaft operably supported in said housing for limited axial movement, cam means operably connected to said shaft for axial movement therewith, a switch mounted adjacent said cam means and adapted for stopping hoisting action of said motor when said load shaft is moved in one direction to a predetermined position, a cam follower operably disposed between said switch and said cam means for actuating said switch when said shaft is in said predetermined position, and spring biasing means operably disposed between said cam means and said housing for biasing said shaft in the other direction axially away from said predetermined position, said housing including an axially adjustable travel member for varying the length of the efiective stroke of said cam means.

2. A hoist control switch as claimed in claim 1 wherein said housing includes an axially adjustable seat member for varying the tension in said spring biasing means, whereby the load on the load shaft necessary to stop hoisting action can be varied.

3. A hoist control switch adapted for stopping the upward hoisting action of a hoist motor when load on the cable of the hoist exceeds a predetermined amount, said switch comprising a housing, a load shaft journaled in an adjustable seat member at one end of said housing and in an adjustable travel member in the other end of said housing permitting axial movement therein, cam means operably connected to said shaft for axial movement therewith, a switch mounted adjacent said cam means and adapted for stopping hoisting action of said motor when said load shaft is moved in one direction to a predetermined position, a cam follower operably disposed between said switch and said cam means for actuating said switch when said shaft is in said predetermined position, and a coil spring seated at its one end against said cam means and at its other end against said adjustable seat member for biasing said shaft in the other direction axially away from said predetermined position.

4. A hoist control switch as claimed in claim 3 wherein said load shaft extends axially outwardly from said housing in said other direction, whereby said switch will be actuated in response to a pushing action on said load shaft.

5. A hoist control switch as claimed in claim 3 wherein said load shaft extends axially outwardly from said housing in said one direction and has a cable attachment thereon, whereby said switch will be actuated in response to a pulling action on said cable attachment.

6. A combined hoist control switch adapted for controlling the downward hoisting action of a hoist motor and for preventing overloading the hoist on upward hoisting action of the hoist motor, said control switch comprising a housing, a load shaft journaled in said housing for axial movement, a load plate mounted on said load shaft for axial movement therewith, a cam carried by said load plate, a first electric switch adapted to control downward hoisting action of said motor, a first cam follower operatively disposed between said first electric switch and said cam for actuating said first electric switch when said cam is moved to a predetermined position, first spring biasing means for biasing said cam to said predetermined position, a second electric switch adapted to control upward hoisting action of said motor, a second cam follower operatively disposed between said second electric switch and said cam for actuating said second electric switch when said cam is moved to a selected position, a second load plate mounted in said housing in axial alignment with said first load plate and positioned to be engaged by the latter when the load shaft has moved a predetermined distance against the biasing action of the first spring biasing means, a second spring biasing means operatively disposed against said second load plate for opposing movement of said cam toward said selected position, and a stop for limiting movement of said second load plate after said cam has reached said selected position.

7. The combination hoist control switch as claimed in claim 6 wherein said housing includes an axially adjustable seat member for varying the tension in said second spring biasing means, whereby the switch may be made selectively responsive to a greater or lesser load on the load shaft for stopping hoisting action.

8. The combination hoist control switch as claimed in claim 6 wherein said housing includes an axially adjustable seat member for varying the tension in said second spring biasing means, whereby the switch may be made selectively responsive to a greater or lesser load on the load shaft for stopping hoisting action, and an axially adjustable travel member for varying the axial length of the effective stroke of said cam means.

9. The combination hoist control switch as claimed in claim 6 wherein said load shaft extends axially outwardly from said housing in said other direction, whereby said switch will be ac tuated in response to a pushing action on said load shaft.

10. The combination hoist control switch as claimed in claim 6 wherein said load shaft exone direction and has a cable attachment there 10 on, whereby said switch will be actuated in response to a pulling action on said cable attachment.

JOHN VJ. HUNT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,890,679 Hallenbeck Dec. 13, 1932 2,159,076 Douglas May 23, 1932 

